The present invention relates to an improvement in diode driver circuits utilized to drive P-I-N diodes, Schottkey diodes or the like which are used in phase modulators, a diode switches or the like, and more particularly, to a high-speed diode driver circuit having low power consumption.
A P-I-N diode having a high reverse voltage and a low forward impedance is used in high-power phase modulators, diode switches and the like. However, since the minority carriers or charges are accumulated in the I layer of a P-I-N diode during the period of forward bias, the diode deteriorates in high-speed response. For this reason, a high-speed P-I-N diode driver circuit must cancel the accumulated carrier in a short period of time when the diode is reverse biassed after being forward biassed. Conversely, when the diode is forward biassed after being reverse biassed, the charges accumulated in the junction barrier during the period of reverse bias must be quickly removed. This function is also required to be produced by a high-speed P-I-N diode driver circuit.
One of the conventional driver circuits having these functions is disclosed in the U.S. Pat. No. 3,922,570 granted to the same applicant on a "Driver Circuit for Modulating Diode". In this circuit, a constant current circuit and a low impedance circuit are connected to a P-I-N diode. When the diode is forward biassed the transistor of the low-impedance circuit is cut off and a constant bias current is supplied from the constant current circuit. When the P-I-N diode is switched so that it is reverse biassed, a large current is supplied from the low impedance circuit to the P-I-N diode to discharge the charges accumulated therein in a short period of time, to thereby achieve high switching speed. This circuit, though excelling in speed, requires a large current to be supplied to the switching transistor. Specifically the current needed to discharge the charges in the junction barrier is fed to the switching transistor by way of a diode connected to the base and the emitter of the transistor of the low impedance circuit. Therefore, this switching current does not permit ready reduction of either power consumption or hardware size.